Castiel felt like his heart was being ripped out of his chest. He had always watched human emotions with such fascination, wondering how it could literally feel like your heart was being torn to shreds when in reality it was still lodged between his lungs. For the first moment that he saw Dean stabbed on a hunt gone wrong, all he could do was sit there in a daze-like state. It was almost like he could not comprehend what he saw in front of him. Dean crumpled to the ground and Castiel completely forgot about the creature running away from the hunters. All he could care about was that Dean was bleeding profusely from his abdomen, his face streaked with intense pain.
Castiel rushed over to Dean, calling his name while he leaned over to put pressure on the wound. The sight of Dean covered in so much blood caused Cas' stomach to lurch.
"Come on, Dean. Hey, hey-Look at me. I need you to try to keep your eyes open. I'll get help, just keep your eyes open." His words were rushed and he watched Dean trying to keep his eyes open. Cas reached one bloody hand into his pocket and retrieved his cell phone and quickly dialed Sam's number.
"Sam! Sam, you need to come here, Dean's hurt. He's hurt really bad and he's bleeding and can't keep his eyes open." He listened for a moment and replied, "No, we're in that storehouse at 5th and Brighte Ave. We don't have any alcohol, and you have to hurry." He hung up the phone so he could use both hands on Dean's stomach. Cas started getting hysterical, and he could not seem to slow the bleeding. He couldn't tell what he was saying and it didn't really matter.
By then, Dean's eyes started to slide shut as his face relaxed. He had a slight smile on his face and looked peaceful as he looked into Castiel's frantic eyes.
"Hey, no Dean you have to keep your eyes open. For me, okay? You can't leave me, you promised. You promised." He choked out a sob on the word "promised".
And Castiel knew at that moment that Dean had died doing what he loved- Saving people, hunting things. The family business.